Titers of live attenuated vaccines are usually thermally unstable. Vaccine preparations are therefore supplied as low-temperature frozen products or lyophilized products. To stabilize them, a chemical stabilizing agent is added to the vaccine solution. Examples of chemical stabilizing agents hitherto known are human albumin, gelatin hydrolyzate, sugar alcohols, amino acids and other non-toxic substances. For example, for this purpose it is known to use a preparation consisting of a basic amino acid such as arginine, lysine or histidine, each 5 W/V% or adding thereto various sugar alcohols such as saccharose, inositol or sorbitol, each 5 W/V% (Jap. Patent Appln. No. 45-1887), a preparation obtained by mixing peptone 5-10 W/V%, arginine or lysine 3 W/V% and saccharose 5 W/V% (Jap. Patent Unexam. Publ. No. 50.2225), a preparation obtained by adding lactose 4 W/V% and sorbitol 2 W/V% to a phosphate buffer solution containing Ca.sup.++ and Mg.sup.++, or adding at least one amino acid 0.005M-0.05M thereto (Jap. Patent Appln. No. 57-81338), a preparation consisting of lactose 5 W/V%, D-sorbitol 1.5 W/V%, dextran 70 0.3W/V%, potassium glutamate 0.048%, disodium phosphate 0.0625 W/V%, potassium phosphate 0.026 W/V%, gelatin 0.3 W/V% and human albumin 0.25 W/V% (Jap. Patent Appln. No. 55-80465), and a preparation wherein a vaccine solution is acidified to pH 6.0-6.5 prior to lyophilization by adding a phosphate buffer solution containing a stabilizing agent comprising a gelatin partial hydrolyzate, M.W. approx. 3,000, sorbitol, saccharose, lactose, maltose, L-glutamate and L-arginine (Jap. Patent Unexam. Publ. No. 57-114527).
Nowadays, vaccines are distributed to tropical countries where there are no refrigerated distribution sytems. In these areas, the vaccine preparations supplied must have heat stability at high temperature. The above known stabilizing agents were not suitable in this regard.
We have found that a live attenuated vaccine shows strong thermostability when lactose, D-sorbitol, saccharose, gelatin hydrolyzate and sodium glutamate at specific ratios of concentration are added to a vaccine virus suspension comprising a medium-199 for cell culture (Morgan, et al., Proc. Soc. Exp. Biol. Med , 73:1-8, 1950) (hereinafter designated as medium-199). Each component thereof has been known as a stabilizing agent for live attenuated vaccines; however, it has never been known that a combination thereof at a specific ratio of concentrations exhibits unexpected thermostability.